public bool Contains(KeyValuePair <K, V> item)
        {
            N node = _redBlackTree.Find(item.Key);

            if (node == null)
            {
                return(false);
            }
            if (ReferenceEquals(node.Value, null))
            {
                return(ReferenceEquals(item.Value, null));
            }
            return(node.Value.Equals(item.Value));
        }
 public N Find(K key)
 {
     if (Compare(key, Minimum) < 0 || Compare(key, Maximum) > 0)
     {
         return(null);
     }
     return(_redBlackTree.Find(key));
 }